Though it's only a little after 9 a.m., Demi Lovato and Nick Jonas are already bickering. They're seated on the terrace at the ritzy Wynn ­brunchery Tableau on a hot Las Vegas summer ­morning, and Lovato has asked Jonas to tack fries onto his meal so she can "have one and not feel bad about myself." When the server arrives, Jonas requests an off-menu egg white omelet -- then casually adds, "You know what? These fries look so good, I might just get them." But Lovato has already changed her mind. "No, no. He's not going to get the fries. I'm watching what he eats. You're ­welcome, honey." She rests a patronizing hand on his shoulder. Jonas shakes his head. "You threw me right under the bus."

Jonas and Lovato, both 23, were Disney Channel charges who started working before they were tweens and have been singing and acting ever since. Each has been, in his and her own way, through the ringer. Jonas' experience with pubescent pop-rockers the Jonas Brothers left him "bruised and a little jaded," says his and Lovato's manager, Phil McIntyre. And Lovato just marked four years of sobriety after a hard-fought battle with mental illness and addiction. But both are now midstride into a second act that, like the first, they're experiencing together -- but this time on their own terms. (And no, they are not, nor have they ever been, romantically entangled.)

"You'd think they're siblings, sometimes more than Nick and I," says Joe Jonas, who briefly dated Lovato in 2010. "I'm so proud of him, man. I'll be honest, I was a bit envious when I saw him catapult into this personal success. And today she's the best version of herself I've ever known." Says Brad Paisley, who recently released the duet "Without a Fight" with Lovato: "Nick and Demi both are great examples of child stars coming of age, becoming really legit, respected musicians. As we all know, not everybody makes that transition."

In May 2015, Lovato and Jonas ­partnered with McIntyre to launch Safehouse Records with help from Island. Their first release: Lovato's fifth album, Confident, which hit No. 2 on the Billboard 200, launched the coy I-kissed-a-girl anthem "Cool for the Summer" and led to grown-woman fare like her new song, "Body Say." The latest release, from June: Jonas' second post-boy-band LP, Last Year Was Complicated, which also notched a No. 2 peak, led by the surging R&B of "Close." On June 29, the pair -- her an established celebrity aiming to stay fresh, him striving to prove men can be pop megastars too -- kicked off a 44-city co-headlining arena tour, Future Now, a "seamless night of music," says Jonas, where they take turns in the spotlight and sometimes back each other up.

It's not their first time together on the road. Lovato recalls getting mad at her straight-laced pal while playing their ­favorite card game on tour in 2008 and 2009: "He'd only say 'BS.' I'd be like, 'Bullshit?! Is that what you mean?'" She also teases Jonas' "little 'fro" on the poster for Disney's Camp Rock, the filming of which solidified their best-friend status almost a decade ago. Today, Lovato, who lives in North Hollywood, is outspoken on social media, candidly discussing her past ­struggles but also ­beefing with Taylor Swift over ­feminist bona fides and incurring the wrath of Mariah Carey's lambs by riding for Ariana Grande. Meanwhile, Jonas, who lives in Sherman Oaks, Calif., explores the ­complexities of modern ­masculinity, both as a glammy top 40 singer and an actor. He plays a gay MMA fighter in the cable drama Kingdom and an aggro fraternity brother in 2016 Sundance success Goat, alongside James Franco.

These days the two enjoy cigars and espresso shots, nerd out over conspiracy theories, watch dumb comedies (but don't really read: "No books," says Jonas) and call each other with any personal crisis. Lovato demurs on the subject of her breakup with Wilmer Valderrama, until June her ­boyfriend of six years, but says Jonas has been there for her and that they've been making music together on the bus. "I work with him on being more vulnerable," says Lovato. "He's doing an awesome job." Replies Jonas: "Thanks."

LOVATO I distanced myself as I was getting involved with self-destructive things. After treatment, I had to have some time sober before I wasn't embarrassed to talk to him. Nick says I sent text messages, but I don't remember shit. The first time we saw each other since that tour was my [2012 Los Angeles] concert at The Greek. We caught up right before the show, then performed. It was an emotional reunion -- I got one of my best friends back.

Nick, what did you think when that happened?

JONAS That we were going to get sued. I mean, it was bad. On top of losing a friend, we have seven dates left, it's a big production, people are expecting to see Demi and that's not going to happen. I was angry, because a week before I pleaded with her to confide in me. We talked on the plane for two hours.

LOVATO (Interrupting.) He's a guy in his 20s and he's famous and he likes to have a lot of fun. Listen, even when he was in a relationship, I was like, "Get out of that. You could f-- anybody that you want right now, so have fun and do that."

LOVATO (Sighs.) I give him a lot of advice. He doesn't always take it.

Nick, your breakup with model-actress Olivia ­Culpo is a big part of your new album's ­narrative...

JONAS It is. I'm in such agony. I'm dying inside! (Laughs.)

When that happened, did you call Demi?

JONAS I internalize things, so we have this rule that we never want to hear about it in a tweet or something. She'd read me the riot act, so she's the third person I call -- my dad, Joe, then Demi. She was like, "Just go, ­create and be free." She also said some other things...

LOVATO (Laughs.) I go, "Honestly, I didn't like her anyway." It's not because she's mean or anything, but he has such a great sense of humor and I want him to be with someone that makes him laugh. I can tell if something's up because he'll close off.

LOVATO It's not on my mind, but I welcome anything. I'll have fun. But a ­relationship ... I won't want that for a long time.

Tell me about your friendship early on, when you were filming Camp Rock.

JONAS Well, for a couple of years there was the Joe and Demi romantic thing, so I'd be this emotional bridge for them. But she and I were productive -- we'd write songs about it. We became even closer because it was never going to be [romantic].

LOVATO There's a song on my first album called "Gonna Get Caught" about how I thought Joe was a player. I remember we were on the bus writing the bridge, and Joe is like, "I think it should have a happy ­ending." I'm like, "No, I don't think it should." And poor Nick is sitting there like, "What are we actually deciding here?"

Did you know how odd your lives were?

LOVATO We joked around that it was Disney High, except we all were shooting shows and really overworking. I joke that I sometimes have PTSD after leaving the channel, because if my schedule starts to get too busy, I rebel and I get bitchy...

JONAS (Mockingly.) No!

LOVATO F-- off. (Laughs.)

Did you feel pushed by adults in your life?

LOVATO Not by my family, but when you're on set, you work like an adult. I always wanted to be the next Shirley Temple, to be the youngest person to ever win a Grammy and an Oscar. It didn't turn out that way. I don't regret it, but I probably won't allow my kids to get into the industry unless it's on their terms.

JONAS I have really musical parents, and my dad was always encouraging, but the desire to get onstage and perform really did come from me. I'd never push my future children.

JONAS (Laughs.) I keep my political views to myself. We both come from conservative households with a religious backbone, but we've both evolved quite a bit in the way we see the world. (To Lovato.) Um, don't you want to tell us about Hillary Clinton?

LOVATO When I went through my shit, I realized it was for a reason -- to make a ­difference. I can share my story a ­million times, but it's not as tangible as going to Capitol Hill. Hillary is in ­support of mental health care and, yeah, I'm a Democrat.

You've had your share of ­Twitter ­drama, but Nick seems to live ­drama-free. Any advice for your friend, Nick?

LOVATO Keep my mouth shut?

You recently stood up for Ariana Grande at Mariah Carey's expense. Did you hear from Mariah or her people?

LOVATO No. (Laughs.) I'm sure she's sitting on diamond records not giving a f-- what I have to say. That's fine. I don't even give a f-- what I have to say. That's why I just say it.

You're visible LGBTQ allies, but some have suggested you're stringing the community along for a fan base. Is that unfair?

JONAS Of course. Think about my past and where my love for performance comes from -- musical theater. And playing this gay fighter in a very macho world for Kingdom, it requires me digging really deep, and I do it with respect and honor.

LOVATO For me, it's a little personal. It's obvious what my ["Cool for the Summer"] lyrics are about. Just because I never said anything bluntly [about experiences with women] doesn't mean I'm exploiting it.

Nick, you spoke at the Stonewall vigil after the Orlando tragedy and got backlash.

JONAS I wouldn't change a thing. That's a moment -- and in general the time we're in in this country -- where unity, support and raising our hand and saying we can make change is what's important, so it's a shame when people make it about something else.

Nick, you go to college in Goat, but neither of you did in real life. If you went now, would you be dorm mates?

LOVATO That would be weird. I don't want to see him f-- other people.

JONAS No, after Goat, I'd make it my ­mission to have an apartment off campus.

LOVATOI wanted to get my own apartment when I was 5 and my mom said no.

JONAS I wonder why.

LOVATO Even then I wanted my own place, so I don't think a dorm would be good for me to share with anybody.